1. Field of the Invention
The present invention relates to a pneumatic tire having an improved profile which improves the ride comfort, low rolling resistance and braking performance.
2. Description of the Related Art
A pneumatic tire has a profile extending from an axially outside shoulder region of the tread portion to the sidewall portion that usually determines the ride comfort, low rolling resistance and braking performance. Referring to FIG. 3, the tire has a tread portion “a” including the shoulder portion b. In case that the profile “e” of the shoulder portion b is modified so as to have a large radius R1 of curvature shown by a virtual line from a radius R2 of curvature, since the shoulder portion b would be rounded, the ride comfort may be improved due to the reduced contact pressure acting on the shoulder portion b. Also, since the rubber thickness disposed on the shoulder portion b tends to be thinner, the rolling resistance of the tire may be decreased due to the small tire weight.
However, such a tire is liable to have an unsatisfactory braking performance due to a small ground contact area of the tread portion.
In order to improve the braking performance of the tire, the tread width may be enlarged so as to have a large ground contact area. However, if the tread width is enlarged, the rubber thickness on the buttress portion disposed in between the tread portion and the sidewall portion is liable to increase, and thereby the rolling resistance may deteriorate due to a heavy tire weight. Moreover, the ride comfort may also deteriorate due to the less deformation of the buttress portion.
In order to improve various performances, a tire having a tread profile that extends along with an involutes line is proposed. The tread profile, for example, has a radius of curvature gradually decreasing from the tire equator to the axially outside of the tire so that the ground contact pressure on the tread portion is uniform in the tire axial direction, and thereby wear resistance and the steering stability may be improved.
However, since such a profile is not sufficiently improved as for the tread shoulder portion and the sidewall portion, the ride comfort, rolling resistance and the braking performance may be deteriorated.